using hiv to cure, not kill. doctors took out millions of emma's disease-fighting white blood cells. then, used a genetically altered hiv virus, which is great at getting into human immune systems, to change those cells into targeted cancer fighters. emma's cells went back in and destroyed the cancer. dr. stephan grupp is a pioneer using hiv to infiltrate the immune system. >> all of the things that make the hiv virus able to cause disease have been removed from this particular virus, so, its only purpose is to put a gene into a cell. for me, it's incredibly exciting. >> reporter: here's emma, just eight months later. doctors can't find any remaining cancer cells. >> she is in a complete remission. she has no leukemia in her body by any test that we can do. even the most sensitive tests. >> she has a ton of energy. she's doing wonderful right now. >> this treatment was a miracle. >> reporter: emma is counting the days till christmas. her parents are busy counting their blessings. now, the treatment does wipe out